Childhood illnesses and behavioral disorders are major health problems in developing countries. This proposal develops a potential approach to solving these global health problems based on a specific nutritional approach that is both conservative and economical. There will be three aims in this large (n=1,200) double blind placebo-controlled, intervention trial of omega-3 fatty acid supplementation of school lunch milk for 8 months. Aim 1: determine if supplementation reduces the incidence or duration of common childhood illnesses. Aim 2: determine if supplementation improves clinically significant behavioral problems: depression and aggression. Aim 3: determine if supplementation improves academic performance as a direct effect on brain function or secondary to reductions of illness or improvements in behaviors. All children enrolled in the study will receive the active agent or placebo. Sub-cohorts of children will be identified for the specific examination of the effects on childhood illnesses, children with behavioral problems and in healthy children. This approach will also allow an examination of the interaction between the behavioral disorders, immunological function and resulting impacts on academic performance. A sub-cohort of children, those who contract an illness, will be intensively examined by a research nurse and physician, if necessary, to determine if there are differences in the severity and duration of illnesses. The sub-cohort of children with clinically significant behavioral problems will be identified using the Child Behavior Checklist and the Thai depression inventory. In this sub-cohort, sensitive and specific behavioral measures of aggression will be performed to assess the efficacy of the supplementation. The Child Behavior Checklist and Thai depression inventory assessments will also serve to estimate the prevalence of these disorders among Thai school children. Finally, the interrelationships between the presence of childhood illnesses, behavioral disorders and academic performance will be examined.